Apparatuses and methods for securing deep brain stimulation leads

ABSTRACT

Various examples are provided for securing deep brain stimulation (DBS) leads. In one example, among others, a DBS cap for securing a DBS lead includes a base ring adapted to be mounted within a counterbore opening formed in the skull, a lead securing element that mounts to the base ring, and a top cover that mounts to the base ring. In another example, a method for securing a DBS lead includes forming a counterbore opening in the skull, securing a DBS cap within the counterbore opening, passing a DBS lead through the DBS cap and the counterbore opening and positioning a tip of the lead in brain tissue, and securing the DBS lead to the DBS cap using an adhesive. The skull opening includes a lower bore, a concentric upper bore, and a step positioned at the interface of the upper and lower bores.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to co-pending U.S. provisionalapplication entitled “APPARATUSES AND METHODS FOR SECURING DEEP BRAINSTIMULATION LEADS” having Ser. No. 61/861,022, filed Aug. 1, 2013, theentirety of which is hereby incorporated by reference.

BACKGROUND

Deep brain stimulation (DBS) is a surgical treatment involving theimplantation of a pulse generator that sends therapeutic electricalimpulses to specific parts of the brain. DBS in precisely selected brainlocations can provide therapeutic benefit for otherwisetreatment-resistant movement and affective disorders, such asParkinson's disease, tremor, dystonia and obsessive-compulsive disorder.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood with reference to thefollowing figures. Matching reference numerals designate correspondingparts throughout the figures, which are not necessarily drawn to scale.

FIG. 1 is an exploded perspective view of an embodiment of a deep brainstimulation (DBS) cap adapted to secure a DBS lead relative to the skullin accordance with various embodiments of the present disclosure.

FIGS. 2A and 2B are schematic views of a patient's skull duringimplantation of a DBS lead and DBS cap, such as the cap shown in FIG. 1in accordance with various embodiments of the present disclosure.

FIG. 3 is a graphical diagram illustrating a test system for evaluationof the DBS cap of FIGS. 1, 2A and 2B in accordance with variousembodiments of the present disclosure.

FIGS. 4A through 4D are plots illustrating examples of test dataobtained for samples of conventional DBS caps utilizing the test systemof FIG. 3 in accordance with various embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The typical DBS system comprises the pulse generator, which is typicallyimplanted within the patient's chest or abdominal wall (e.g., under theskin below the clavicle), a DBS lead that is implanted in the brainthrough an burr hole in the skull, and a connection cable (sometimesreferred to as the “extension”) that is tunneled under the skin toconnect the DBS lead to the pulse generator. The DBS lead typicallycomprises a series of elongated conductive wires surrounded by polymerinsulation. The polymer-encased wires are connected at each end of thelead to a series of exposed electrodes. The electrodes at the distal endof the lead are implanted in contact with desired regions of the brainto deliver the therapeutic electrical impulses. In the typical case, thetip of the lead is positioned in a region deep within the brain. Inorder to obtain the desired outcome from the system, it is critical thatthe lead tip is positioned at a precise location within the brain bothduring the surgical procedure and thereafter.

A DBS cap is typically attached to the skull at the burr hole site andused to secure the DBS lead to the skull at the entry site to ensurethat the intracranial lead does not migrate and the positions of thetherapeutic contacts remain constant in the brain. While such capsnormally incorporate locking elements that are intended to preventmovement of the lead, the locking elements often fail to preventmigration of the lead either intra-operatively while the lead is beingsecured, or post-operatively due to some inward or outward axial force.If significant migration of the intracranial electrodes occurs, thebeneficial therapeutic effect of DBS can be lost, resulting in the needfor reprogramming of the device, or even further surgical interventionto replace the displaced DBS lead.

In addition to their poor performance at preventing DBS lead migration,existing DBS cap designs protrude from the outer surface of the skull.This cap protrusion produces a poor cosmetic result and predisposespatients to the development of delayed scalp erosions with exposure andbacterial contamination of implanted DBS hardware. This serious, delayedcomplication of DBS surgery requires surgical intervention to repair thescalp erosion and, when purulent or life threatening infections result,may require removal of the DBS hardware—with loss of therapeuticbenefit—in order to eradicate the infection. The relatively commonoccurrence of scalp erosion at the site of a protruding DBS cap warrantsthe development of a DBS cap that can be readily installed flush withthe outer surface of the skull to eliminate cap protrusion and minimizethe risk for development of this serious complication.

As described above, it would be desirable to have a more effectiveapparatus and method for securing a deep brain stimulation (DBS) leadthat ensures that the lead and its therapeutic contacts in the brain donot migrate. Disclosed herein are examples of such apparatuses andmethods. In one embodiment, an apparatus comprises a DBS cap that mountsto the skull under the scalp and secures a DBS lead with a securingelement that incorporates an adhesive that prevents the lead from movingrelative to the cap and, therefore, the skull. In further embodiments,the DBS cap sits within a counterbore opening formed in the skull and issubstantially flush with the outer surface of the skull so as to providean improved aesthetic result and to mitigate delayed scalp irritationand erosion.

In the following disclosure, various specific embodiments are described.It is to be understood that those embodiments are exampleimplementations of the disclosed inventions and that alternativeembodiments are possible. All such embodiments are intended to fallwithin the scope of this disclosure.

FIG. 1 illustrates an embodiment of a DBS cap 10. As shown in thefigure, the cap 10 generally comprises a base ring 12, a lead securingelement 14, and a top cover 16. Each of these components can be made ofa suitable biocompatible material. In some embodiments, the componentsare made of a metal material, such as stainless steel or titanium, or apolymeric material, such as polycarbonate, polyurethane,polydimethylsiloxane, or a similar biocompatible polymer.

Irrespective of the material used to fabricate the base ring 12, thebase ring is generally ring-shaped. Accordingly, the base ring 12 isgenerally circular, i.e., has a generally circular outer periphery 18,and includes an inner opening 20 that extends from a top surface 22 ofthe ring to a bottom surface 24 of the ring. Notably, the base ring 12is devoid of any tabs or wings that extend outward from its generallycircular outer periphery 18. The base ring 12 is sized so as to fitwithin a counterbore opening formed in the skull of the patient. Invarious implementations, the counterbore opening can be countersunk. Insome embodiments, the base ring 12 has an outer diameter ofapproximately 20 to 30 mm and a height dimension (i.e., the distancebetween the top and bottom surfaces 22, 24) of approximately 2 to 6 mm.The dimensions of the inner opening 20 can be varied as desired butnormally are large enough to facilitate implantation of the DBS leadwithin the brain tissue and, therefore, large enough to accommodate anyapparatus (e.g., guides) used for that purpose. In some embodiments, theinner opening 20 has a diameter of approximately 12 to 16 mm.

As is also shown in FIG. 1, the base ring 12 includes concentriccircular grooves or depressions that are located at the interfacebetween the inner opening 20 and the top surface 22 of the ring. In someembodiments, these depressions include a first, lower or innerdepression 26 that is adapted to receive the lead securing element 14and a second, upper or outer depression 28 that is adapted to receivethe top cover 16. As is apparent from FIG. 1, the inner (or lower)depression 26 is smaller than the outer (or upper) depression 28. Insome embodiments, the inner depression 26 is approximately 14 to 16 mmin diameter and the outer depression 28 is approximately 14 to 18 mm indiameter. In some embodiments the inner depression 26 or outerdepression 28 or both may include protrusions or fittings which providea friction or snap fit of the mating part.

The base ring 12 further comprises mounting holes 29 that are adapted toreceive fasteners, such as bone screws, for the purpose of affixing thebase ring within a counterbore opening formed in the skull. The mountingholes 29 extend from the top surface 22 of the ring to its bottomsurface 24. In some embodiments, two such mounting holes 29 can beprovided. In some embodiments, such mounting holes 29 includeprotrusions or fittings to retain the screws during fastening.

With further reference to FIG. 1, the lead securing element 14 generallyincludes two opposed pivotable or otherwise translatable members 30 and32 that are adapted to close like a pair of jaws to clamp inner edges 34and 36 onto a DBS lead that extends through the inner opening 20 andinto the brain. As indicated in the figure, the lead securing element 14is also generally circular and therefore comprises a generally circularouter periphery 38, which, in some embodiments, is defined by bothmembers 30, 32 of the element. When the two members 30, 32 are pivotedtoward each other in the directions identified by the arrows in FIG. 1to clamp a DBS lead, the outer periphery 38 of the lead securing element14 can fit within the inner depression 26 of the base ring 12. As isfurther illustrated in FIG. 1, one of the members (member 30 in thisexample) can be provided with multiple indentations 40 along its inneredge 34 in which the DBS lead can be positioned. In some embodiments,the indentations 40 are curved and have a radius of curvature that isslightly smaller than the radius of the DBS lead so as to pinch thepolymer sheath of the lead to more securely hold it in place in such away that the internal wires are not crushed or otherwise damaged. Insome embodiments, the radius of curvature of the indentations 40 isapproximately 0.5 to 2 mm.

While the lead securing element 14 is designed to secure the DBS lead inplace, migration, such as pull out, can still occur due to therelatively slippery nature of the polymer sheath of the DBS lead. Toprevent such migration, one or both of the inner edges 34, 36 of theelement members 30, 32 can be provided with a layer of adhesive that canmore securely hold the DBS lead. In some embodiments, the adhesive is alight-curable adhesive that cures when exposed to light within aparticular wavelength band, e.g., the ultraviolet (UV) light wavelengthband. Moisture-curable and/or air-curable adhesives can also be used asthe adhesive. In some embodiments, the adhesive can be covered with aprotective membrane (e.g., a protective polymeric membrane) that isremoved prior to closing of the members 30, 32. It is noted that furtheradhesive can be provided on the outer periphery 38 of the lead securingelement 14 and/or the inner depression 26 of the base ring 12 to securethe lead securing element to the base ring.

The top cover 16 is adapted to cover the inner opening 20 of the basering 12 and, therefore, the opening formed through the patient's skull.As shown in FIG. 1, the top cover 16 can be generally circular andtherefore have a circular outer periphery 42. Once the DBS lead has beenpositioned as desired and secured by the securing element (e.g., bycuring the adhesive provided thereon), the top cover 16 can bepositioned within the outer depression 28 of the base ring 12. In someembodiments, the outer periphery 42 of the top cover 16 and/or the outerdepression 28 of the base ring 12 can also be provided with an adhesivethat secures the cover in place on the base ring. As is illustrated inFIG. 1, the outer periphery 42 of the top cover 16 can include one ormore notches 44 in which the DBS lead can be positioned so as to avoidcrimping the lead as it exits the DBS cap 10.

To implant a DBS lead, a counterbore opening is formed through theskull, such as the opening 50 illustrated in FIG. 2A. As is apparentfrom that figure, the opening 50 extends through the skull 52 andincludes a lower bore 54 having a relatively small diameter and aconcentric upper bore 56 having a relatively larger diameter. In someembodiments, the opening 50 can be formed using a sterile counterboredrill bit. In some embodiments, the depth of the counterbore is limitedby a collar or other indicator on the bit. Forming such an opening 50creates a step 58 at the interface of the two bores 54, 56 that cansupport the base ring 12. Once the opening 50 has been formed, the basering 12 can be inserted into the opening and secured in place withfasteners, such as screws. At this point, the DBS lead can be implantedinto the brain through the inner opening 20 (see FIG. 1) of the basering 12 and through the opening 50 in the skull 52. Once the tip of theDBS lead has been positioned as desired, the lead can be secured inplace with the lead securing element 14 and its adhesive, and the topcover 16 can be connected to the base ring 12. FIG. 2B illustrates anexample result showing the DBS cap 10 in place within the opening 50 anda DBS lead 60 extending into the brain tissue 62 and out through the DBScap.

There are several procedure-related and hardware-related complicationsthat may occur as a result of DBS therapy. One such complication is leadmigration. Lead migration has been defined as unintended movement of theDBS lead following the securing of the lead to the skull with a cappingdevice or other methodology. There are several potential causes of DBSlead migration including failure of the clamping mechanism, motion ofthe brain, movement of the cranium, trauma to the skull, and iatrogenicissues (e.g. the lead is accidentally tugged on during pulse generatorimplantation).

To study the dynamic stability of DBS leads, a model system was used tomeasure real-time acceleration and displacement of a laboratory basedartificial brain and skull that was fitted with an implanted DBS lead.Impact testing recorded the lead position, accelerations of the brainand skull in three axes, and real-time measurements of the impact force.In addition, the tensile strength of the lead clamping was alsocollected to estimate the force required to displace the DBS lead when aDBS cap was utilized.

Referring to FIG. 3, shown is an example of a test system 300 used totest the stability of the DBS leads. All testing was performed using thecustom-built platform, which was designed to rotate around a PVC moldedskull 302 mounted on a molded silicone pedestal 304 to simulate asemirigid neck. The pedestal was attached to a base and the neckstiffness was modified by varying the length of a PVC stiffener. Thetest system includes a support frame 306 supporting an impact arm 308with a weight attached to the distal end. A protractor 310 can be usedto provide a repeatable release height from which the impact arm 308 canbe swung. The impact force was adjusted by increasing or decreasing theangle of the impact arm 308 prior to releasing it. The length of theimpact arm 308 may also be adjusted to reach different regions on theskull 302. The skull 302 can be mounted horizontally on the pedestal 304to measured blows from all directions.

The brain inside the skull 302 was molded using 0.9% agarose gel (AcrosOrganics) with 0.9% sodium chloride to facilitate proper electricalconductivity. The 0.9% agarose gel was chosen based upon a similartexture and consistency to brain tissue. A mold was created usingstandard silicone compounds from the model brain t was designed to mateto the skull. After insertion of the molded agarose brain, the cavitywas sealed and filled with saline which was used to simulatecerebrospinal fluid.

The model skull 302 was modified to include a standard burr hole for theDBS lead. The burr hole was placed distal to the midline (about 3 cm)and posterior to the coronal suture (about 1 cm). The impact systemincluded an impact arm 308 that was 80 cm in length and a protractorthat was a sensor. This protractor 310 was used to measure repeatedstrikes to the artificial brain. The height of the impact point could beadjusted to provide the desired impact point on the model skull. A layerof polymer clay approximately 1 cm thick was placed on the surface ofthe impact point to approximate the reduction in impulse that might beexpected in the human.

The impact force was measured using an Omega DLC101 force sensor thatwas threaded onto the weight attached to the distal end of the impactarm 308. This assembly formed the impact surface used to strike themodel skull 302. The load cell can measure the impact force.Acceleration of the brain and skull were measured independently throughthe use of two Omega model ACC-301 three-axis accelerometers. One 3-axisaccelerometer was rigidly attached to the top of the skull, and theother 3-axis accelerometer was suspended (during casting) in the agarosebrain.

The DBS lead position was measured using a system based on monitoringcapacitance changes between the lead, and a large flat plate molded intothe gelatin near the electrode position at the base of the model brain.The electrode position was monitored in real time using a custom-builtphase-sensitive circuit that measured the phase shift caused bycapacitance changes resulting from the motion between the electrodes.This method provided excellent sensitivity for small movements (i.e. submillimeter movements) while providing improved signal-to-noise ratiosthrough the use of a frequency sensitive lock-in signal detectionsystem.

Each of the 3-axis acceleration signals from both the skull and brain,as well as the DBS lead position and impact force signals were allsampled using a Measurement Computing USB-1608 FS. The signals can beprovided to a computing device 312 through wired and/or wirelessconnections, where the values can be collected and later analyzed using,e.g., custom Matlab® software. An electronic trigger sensed the positionof the impact arm 308 just prior to impact with the skull 302. Thistrigger synchronized data collection with the dynamic force andacceleration so that the maximum meaningful data could be collected fora given time and a particular buffer. Acceleration data was processed byFourier filtering and integration of the acceleration data to providetime-dependent force and position. The test system 300 generated forceand position data for both the brain and the skull. The data wasgraphically represented as being relative to the measured dynamic impactforce. Rotational accelerations were not examined, and were minimized byexamining impacts that occurred radial to the axis of the skull 302.

Impact testing was performed by drawing the impact arm 308 back to thedesired position, followed by release of the impact arm 308. In eachtrial, impact data was obtained for a series of impact events withincreasing impact force. Each subsequent impact was obtained byincreasing the angle of the impact arm 308 by one degree for each impactevent. During each impact event, total axial lead motion relative to thereference point in the gelatin brain was recorded. Also recorded was theimpact force and acceleration with respect to time. The limit ofdetection for the axial lead motion was approximately 0.3 mm. The peakimpact force measured for the impact when the DBS lead first moved wasdesignated as the threshold force. For those trials where motion wasnoted, testing was continued by increasing impact force until theapplied force was twice the threshold force (if present).

DBS lead movement was recorded based upon capacitance change withdistance. The distance of the electrical DBS lead from a reference plateembedded in the cast gelatin brain affects the electrical impedance ofthe phase-sensitive circuit formed by the plate and the implantedelectrode. The impedance change was dominated by the change incapacitance resulting from movement of the electrode with respect to thereference plate. The distance between the electrode and reference platewas proportional to the phase shift between an AC voltage appliedbetween the DBS lead and the plate, and the resulting current flow. Thephase variations can be measured using a lock-in amplifier that monitorsthe current relative to the applied voltage.

The measurement of the distance moved was calibrated using a similargelatin cast placed in a beaker from the same batch as each of theoriginal gelatin molds. The DBS lead was carefully moved through aseries of known distances, and measurements taken, to provide acalibration curve that related the distance to a phase signal obtainedby the lock-in detection. The use of an AC signal along with the lock-indetection provided immunity to noise. The estimated maximum error inconversion from voltage to distance was approximately ±0.5 mm. Relativemotion was detectable at approximately 0.3 mm. The motion of theelectrode could be reliably detected down to less than 0.3 mm.

While the lock-in detection provided excellent sensitivity and noiserejection, it imposed a limitation on time resolution. The lock-inamplifier used to detect phase shifts imposed a measurement timeconstant on the order of about 300 msec. The motion of the brainrelative to the skull 302 was measured using a scale of 10's ofmilliseconds. Thus, while the motion of the DBS lead could not befollowed on the same time scale as the other monitored information, thetotal movement was measured by the difference in output from the startto finish of the impact measurement. Thus, the net motion for eachimpact was reported.

In addition, the effect of tissue on the impact was considered as apotential source of error. The tissue effect was modeled by adding 1 cmof polymer clay to the impact surface. The accelerations involved weremodeled to be similar to those found in small traumatic impacts such as,e.g., a bump to a head.

Tensile testing of the DBS lead was performed using the same model loadcell used for impact measurements, but reconfigured for tensilemeasurement. The DBS lead was attached to the load cell with a couplingthat allowed free off-axis motion (or swiveling) to minimize the effectof any non-axial motion. As the lead was pulled, the tensile force wasincreased over time. At the point where the lead pulled free of the leadsecuring element 14 (FIG. 1), the force decreased. This was due to thestarting friction of the lead securing element 14 being set higher thanthe slipping friction. The tensile force applied at the moment offailure was recorded as the holding force of the lead securing element14.

The DBS leads were secured in a DBS cap 10 (FIG. 1) in the same fashionas they would have been for clinical use in humans. The DBS cap 10 wasutilized including the base ring 12, the lead securing element 14, andthe top cover 16 of FIG. 1. As the DBS lead passed through the leadsecuring element 14, it was routed perpendicular to the clamping surfaceas illustrated in FIG. 2B, so as to maximize the holding force.

For each trial, the tensile holding force was measured both with andwithout a DBS cap 10 present. In this manner, the holding force of thelead securing element 14 could be distinguished from the holding forcethat resulted from friction between the gelatin and the DBS lead.

Only one angle of impact relative to the skull 302 (FIG. 3) wasperformed. The impact testing was applied to a single location on thesame side of the skull 302 as the DBS lead. FIG. 4A shows the motion ofthe electrode of the DBS lead versus the peak impact force for 5 trials.The first two trials (402 and 404) revealed a large motion (2-3 mm)after 60N of peak impact force. The following 3 trials (406, 408 and410) demonstrated less than 0.5 mm of movement even at the maximumavailable impact force of approximately 170 N (about 38 lbs-force). Notethat the plotted lines between measurement points are present to helpdistinguish the measured data. Interestingly, although there was notlarge scale motion, there was small movement (about 0.3 mm) in 2 ofthose 3 trials 406 and 410). This small movement tended to be reversedon subsequent impacts. During these three trials (406, 408 and 410), itwas noted that the DBS lead had been installed in such a way that it was“bent” between the lead securing element 14 (FIGS. 1, 2A and 2B) and thebrain. This may have been due to a kink in the DBS lead or to poortechnique during installation, such as moving the DBS lead duringfastening of the lead securing element 14.

Tensile tests were performed using three separate DBS caps 10 (FIG. 1).Each DBS cap 10 was tested three times to simulate opening and closingof the lead securing element 14 (FIG. 1) during adjustment. This wasdone purposely as this may occur in clinical DBS applications. FIG. 4Bis a plot illustrating raw data of force as a function of time for asample trial with the DBS cap 10. Positive values represent acompressive force, while negative values represent tension. Note thatthe tensile force is drastically reduced (412) when the DBS lead slipsout of place. Since this is a tensile test, a negative deviationindicates a greater pulling force. The example of FIG. 4B illustratesthat at time 1 millisecond, the lead displaced with a tensile force ofslightly less that 1.35 N (0.3 lbs-force). The complete results aresummarized in FIG. 4C, with the peak force plotted against the first,second, and third “re-closures” (number of times used) of the leadsecuring element 14. Square-shaped points (414) in FIG. 4C areindividual data points for the tests, diamond-shaped points (416) arethe mean results for the three DBS caps 10, and the bars indicate thesingle standard deviation. There was variability observed across thetrials, however, less than 2 N of force (0.5 lbs-force) was consistentlyrequired to result in lead movement (tensile holding strength).

Tensile testing using only the DBS lead implanted in the gelatin brain(without any lead securing element 14 at the skull 302) was alsoperformed. FIG. 4D shows the peak tensile force observed when pullingthe DBS lead out of the gel brain 302 (FIG. 3). Square-shaped points(418) represent individual data points from 10 trials. Thediamond-shaped point (420) represents the mean with the error barshowing a standard deviation. As shown in FIG. 4D, the mean tensileholding force without the clamp was 0.58 N (0.13 lbs-force).

The impact data obtained using the test system 300 of FIG. 3 reveal thatthe clamp was a robust solution for moderate head impacts.Interestingly, the DBS leads were more stable in the tests when a smallbend was inadvertently introduced. It is unlikely that this would be thecase clinically. In the laboratory simulation, the DBS leads were placedby hand, without the benefit of fixturing. That is, no halo fixture wasattached to the skull during DBS lead placement. The stylus with the DBSlead was inserted by hand without being guided by the typical mechanicalguidance used for surgical cases. Thus any inadvertent non-axial motion,particularly between placing the electrode and clamping, may have led toa small “bend” in the electrode wire such that it was clamped at a pointslightly non-axial to the lead. While a stylus is typically used, thispart of the assembly had to be removed prior to clamping in thelaboratory. The tested system was therefore less rigid.

The results revealed less electrode motion when the DBS lead had someslack. This finding may be better understood when considering the motionof the brain and skull after impact. Following impact, the relativemotion between the brain and skull 302 (FIG. 3) was up to 5 mm. Therelative motion between the brain and the skull 302, where the DBS leadwas fixed, could lead to a “pulling” of the DBS lead away from itsinitial position. Geometrically, this would result in a curve in thelead. A bend in the lead between the brain and skull may be desirable;however it is unlikely that this could be accomplished during surgery,given the efforts to carefully and accurately place a DBS lead.

The results also revealed that lead motion in the model system did nottranslate to similar observations in the human clinical setting.Specifically, careful examination of follow-up scans revealed that leaddisplacement in the human series was associated with little (or no) leadcurvature. This suggests the possibility that many of the displacementsuncovered by the model system may have been clinically insignificant.

The tensile holding capability of the DBS cap 10 (FIG. 1) was also foundto be small. The holding force for tensile “tugging” on the DBS lead wasapproximately 2 N with approximately 0.6 N derived from friction betweenthe brain and the DBS lead. This force is small enough that eveninadvertent “tugs” on the DBS lead during surgery could result in axialdisplacement. It is also likely that in vivo friction between the brainand the DBS lead is different in the human as compared to the modelsystem, and that the human brain may form a stronger bond than gelatin.

Occasionally, a neurosurgeon may open and repeat closure of a leadsecuring element 14 (FIG. 1) in the DBS cap 10, especially if DBS leadrepositioning is needed. The effectiveness of the repeat closure of thelead securing element 14 by testing the tensile securing ability of thesame lead securing element 14 over three trials was examined. The meanholding strength steadily decreased following each of the trials, with amean reduction of about 14% per trial. Although the holding strengthdecreased, there was a noted scattering in the data from clamp to clamp,rendering the results difficult to interpret. Interestingly, whileclinically neurosurgeons have suggested that repeated clamp use resultsin reduced effectiveness, in some of trials, the effectiveness actuallyimproved after repeated use.

The DBS cap 10 can be easily used, can be re-usable if repositioning DBSleads is needed, and can be successfully utilized in clinical practice.In addition, it can overcome the issues of poor tensile holding powerdemonstrated in the measurements. By adding a layer of adhesive, theholding strength can be increased, limited only by the type andapplication method of the adhesive. An additional advantage is that theembodiments disclosed can result in a cap that is substantially flushwith the surface of the skull, resulting in better cosmetic appearanceand markedly reducing the likelihood of scalp erosions.

It should be emphasized that the above-described embodiments of thepresent disclosure are merely possible examples of implementations setforth for a clear understanding of the principles of the disclosure.Many variations and modifications may be made to the above-describedembodiment(s) without departing substantially from the spirit andprinciples of the disclosure. All such modifications and variations areintended to be included herein within the scope of this disclosure andprotected by the following claims.

It should be noted that ratios, concentrations, amounts, and othernumerical data may be expressed herein in a range format. It is to beunderstood that such a range format is used for convenience and brevity,and thus, should be interpreted in a flexible manner to include not onlythe numerical values explicitly recited as the limits of the range, butalso to include all the individual numerical values or sub-rangesencompassed within that range as if each numerical value and sub-rangeis explicitly recited. To illustrate, a concentration range of “about0.1% to about 5%” should be interpreted to include not only theexplicitly recited concentration of about 0.1 wt % to about 5 wt %, butalso include individual concentrations (e.g., 1%, 2%, 3%, and 4%) andthe sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within theindicated range. The term “about” can include traditional roundingaccording to significant figures of numerical values. In addition, thephrase “about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”.

Claimed are:
 1. A deep brain stimulation (DBS) cap for securing a DBSlead, the cap comprising: a base ring adapted to be mounted within acounterbore opening formed in a skull; a lead securing element thatmounts to the base ring; and a top cover that mounts to the base ring.2. The DBS cap of claim 1, wherein the base ring is generally circular.3. The DBS cap of claim 2, wherein the base ring is devoid of any tabsor wings that extend outward from its outer periphery.
 4. The DBS cap ofclaim 1, wherein the base ring includes an inner opening that extendsfrom its top surface to its bottom surface.
 5. The DBS cap of claim 1,wherein the base ring includes at least one mounting hole that isadapted to receive a fastener.
 6. The DBS cap of claim 1, wherein thebase ring includes a lower depression adapted to receive the leadsecuring element and a concentric upper depression adapted to receivethe top cover.
 7. The DBS cap of claim 6, further comprising an adhesiveused to secure the lead securing element in place within the lowerdepression of the base ring.
 8. The DBS cap of claim 7, wherein theadhesive is used to secure the top cover in place within the upperdepression of the base ring.
 9. The DBS cap of claim 7, wherein theadhesive is a moisture-curable adhesive, an air-curable adhesive, or alight-curable adhesive.
 10. The DBS cap of claim 1, wherein the leadsecuring element comprises opposing members that are adapted to clamponto the DBS lead.
 11. The DBS cap of claim 10, wherein an inner edge ofone of the opposing members includes indentations that are adapted toreceive the DBS lead.
 12. The DBS cap of claim 10, wherein an inner edgeof one of the opposing members includes an adhesive that can be used tosecure the DBS lead in place within the lead securing element.
 13. TheDBS cap of claim 12, wherein the adhesive is a moisture-curableadhesive, an air-curable adhesive, or a light-curable adhesive.
 14. TheDBS cap of claim 1, wherein the top cover comprises a notch providedwithin its periphery that is adapted to receive the DBS lead and enableit to pass through the DBS cap.
 15. A method for securing a deep brainstimulation (DBS) lead, the method comprising: forming a counterboreopening in a skull, the opening including a lower bore, a concentricupper bore, and a step positioned at an interface of the upper and lowerbores; securing a DBS cap within the counterbore opening; passing a DBSlead through the DBS cap and the counterbore opening and positioning atip of the lead in brain tissue; and securing the DBS lead to the DBScap using an adhesive.
 16. The method of claim 15, wherein forming thecounterbore opening comprises drilling the opening using a counterboringdrill bit.
 17. The method of claim 15, wherein securing the DBS capcomprises affixing the DBS cap to the step provided within thecounterbore opening.
 18. The method of claim 15, wherein securing theDBS lead further comprises clamping the DBS lead with a lead securingelement of the DBS cap.
 19. The method of claim 18, wherein the adhesiveis provided on an inner edge of the lead securing element and whereinsecuring the DBS lead further comprises activating the adhesive.
 20. Themethod of claim 19, wherein activating the adhesive comprises curing theadhesive using ultraviolet light.
 21. The method of claim 15, furthercomprising sealing the counterbore opening with a top cover of the DBScap through which the DBS lead passes.
 22. The method of claim 21,wherein sealing the counterbore opening comprises sealing the top coverto the remainder of the DBS cap with an adhesive.